Generally, a progress of ozonation is one of the highest process levels in the field of purifying water. In the process of purifying water, ozone (O3) can dismantle and remove taste and odor materials and THM (trihalomathane) precursor, can erase color, insolubilize iron and manganese, and can get rid of a very small amount of various harmful materials with a strong oxidation power so that it has a broad range of use in the field of purifying water. Thanks to those effects, a large number of filtration plants in the world introduce and operate the progress of ozonation.
According to the injecting point, ozone is classified as three steps: pre-ozonation, intermediate-ozonation, post-ozonation. Pre-ozonation is processed on the stage of water-intake and intermediate-ozonation is processed after the depositing reservoir specifically injecting ozone on the front side of sand filter paper. Post-ozonation is to inject ozone on the latter part of sand filter paper. Generally, a granule activated carbon process follows after post-ozonation so that the country operates it as a biological activated carbon process.
In the process of filtration system, ozone is produced with the materials such as air or oxygen through the ozonizer and is used after liquefying gaseous ozone through the diffuser (or ejector). However, ozone is not 100% completely dissolved in water so the residual ozone is processed to be conveyed from the top of the sealed ozone contractor to residual ozone destroyer after contact with water.
As stated above, it is widely used in the process of purifying water because of the effect of improving water quality. However, if you inhale gaseous ozone for a long time, it reaches to the fine organs and alveolus and causes pulmonary emphysema, and it may cause abnormal chromosome or alter red blood cells by producing peroxides with reaction on body material. Therefore, workers in the filtration plant should be aware of not being exposed to the gaseous ozone.
Ozone contractor currently being operated, is able to process residual ozone inside the contractor because of its sealed shape, but it creates a lot of problems while proceeding to the next step of ozone contact tank. Ozone is volatile when water with residual ozone is exposed to the atmosphere. In addition, in the post-ozonation, ozone is injected to maintain concentration of the residual ozone in the outflow at 0.03˜0.4 mg/L, and granule activated carbon which will be applied to the next progress of ozone contact tank is downstream (move from up to down). Therefore, the upper part of granule activated carbon is open so that it is inevitable to smell ozone.
Because ozone is heavier than air, ozone odor is not discharged to the outside but stays in the building. For that reason, the health of managers working in the granule activated carbon building is threatened, and high-priced corrosion resistant materials should be used to resist against strong corrosiveness of ozone for the metal construction subsidiary materials within granule activated carbon.
Although there is a case to cover the upper side of granule activated carbon in order not to be exposed to the ozone gas, it has some difficulties to confirm directly the state of operation and the management. Also it makes workers and visitors of the filtration plant recognize that the filtration process is a dangerous facility. The residual ozone can be eliminated by injecting chemicals such as calcium thiosulfate, sodium sulfite, and hydrogen peroxide, however, which needs to raise operating expenses and can not be a green environmental device by using chemicals.